Radium Sorption on Sandy and Clayey Sediments of the Upper Saxon Elbe River Valley

The interaction of radium with characteristic sediments of the upper Saxon Elbe river valley was investigated with a two-fold aim: to provide key data for transport modelling within the framework of mining site restoration and to study the influence of barium-radium-sulfate coprecipitation on the radium adsorption behaviour. For this purpose sorption measurements were carried out on site-specific sediments (different kinds of sandstone, claystone and lime marl) using (1) original low-mineralized groundwater of this area, (2) typical acidic mine water coming from sulfuric acid residues of a former in-situ leaching process (~3 g/L SO₄^2-, pH _ 2.5) and (3) groundwater which was contaminated by 2% mine water. The distribution ratios (R_d) were determined by batch experiments using an 8 weeks' equilibration at aquifer temperature (14C).

Radium sorption from pure and slightly contaminated groundwater onto limonite-rich turonian sandstone is characterized by relatively low distribution ratios (60-180 mL/g). When contacted with mine water, the sorption was enhanced by more than 20-fold compared to the pure and contaminated groundwaters. For the typical lime marl, the strongest sorption occured from the groundwater (390-520 mL/g) and a slightly reduced sorption took place from the acidic mine water.

In addition, the radium sorption was studied as a function of the Ba²⁺ and SO₄^2- concentration. The results were discussed in terms of the ion product and the solubility product. Conclusions were drawn regarding the predominant sorption mechanisms: coprecipitation, surface complexation and ion exchange.

The long-term migration behaviour in the aquifers of the south-east Saxon Elbe basin was calculated on the basis of Hadermanns' equation, considering convection, dispersion, retardation and radioactive decay.